\name{formula.gamlss}
\alias{formula.gamlss}

\title{Extract the Model Formula in a GAMLSS fitted model}
\description{\code{formula.gamlss} is the GAMLSS specific method for the generic function \code{formula} which extracts the model formula
     from objects returned by modelling functions.  
     }
\usage{
\method{formula}{gamlss}(x, what = c("mu", "sigma", "nu", "tau"), ... )
}

\arguments{
  \item{x}{a GAMLSS fitted model }
  \item{what}{which parameter coefficient is required, default \code{what="mu"} }
  \item{\dots}{for extra arguments }
}

\value{
 Returns a model formula 
}
\references{Rigby, R. A. and  Stasinopoulos D. M. (2005). Generalized additive models for location, scale and shape,(with discussion), 
\emph{Appl. Statist.}, \bold{54}, part 3, pp 507-554.

Stasinopoulos D. M., Rigby R.A. and Akantziliotou C. (2006) Instructions on how to use the GAMLSS package in R.
Accompanying documentation in the current GAMLSS  help files, (see also  \url{http://www.gamlss.org/}). 

Stasinopoulos D. M. Rigby R.A. (2007) Generalized additive models for location scale and shape (GAMLSS) in R.
\emph{Journal of Statistical Software}, Vol. \bold{23}, Issue 7, Dec 2007, \url{http://www.jstatsoft.org/v23/i07}.
}

\author{  Mikis Stasinopoulos \email{d.stasinopoulos@londonmet.ac.uk} }

 
\seealso{\code{\link{gamlss}}, \code{\link{deviance.gamlss}},  \code{\link{fitted.gamlss}}}
\examples{
data(aids)
h<-gamlss(y~poly(x,3)+qrt, family=PO, data=aids) # 
formula(h,"mu")
rm(h)
}
\keyword{regression}% 
